diff --git a/gtk-3.20/scss/_functions.scss b/gtk-3.20/scss/_functions.scss
index d0ea685..4319c35 100755
--- a/gtk-3.20/scss/_functions.scss
+++ b/gtk-3.20/scss/_functions.scss
@@ -77,3 +77,19 @@ $modules: () !default;
 
     &:active:disabled, &:checked:disabled { border-color: border_normal($color); }
 }
+
+@function _text_shadow_color($tc: $fg_color, $bg: $bg_color) {
+    //
+    // calculate the color of text shadows
+    //
+    // $tc is the text color
+    // $bg is the background color
+    //
+    $_lbg: lightness($bg)/100%;
+    @if lightness($tc) < 50% {
+        @return transparentize(white, 1-$_lbg/($_lbg*1.3));
+    }
+    @else {
+        @return transparentize(black, $_lbg*0.8);
+    }
+}